This study is a multi-site (Detroit, MI; Los Angeles, CA; Philadelphia, PA, and Washington, DC), two-group randomized controlled trial testing a two-session intervention designed to increase motivation for adherence to antiretroviral treatment (ART) among youth living with HIV (YLH) newly recommended to begin medications. Participants are randomized to receive the intervention, Motivational Enhancement System for Adherence (MESA), or the control condition, System for Health (SH: healthy eating and physical activity information). Both groups receive the standard of care regarding the initiation of ART. ART adherence (visual analog scale and hair sample assay) and health outcomes (viral load results, and CD4 counts) are assessed. Additionally, potential mediators (HIV knowledge, motivation for adherence, and self-efficacy for adherence) and predictors of intervention response (substance abuse, mental health symptoms, executive functioning, and stressful life events) are assessed.